Sahih Muslim Book 25, Hadith Number 5365.

Chapter : Disapproval of saying: “It is I” In response to one’s inquiry while seeking permission to get in the house.

This hadith has been transmitted on the authority of Shu’ba with a slight variation of wording and that is: The Holy Prophet (may peace be upon him) uttered these words: It is I, it is I.” in the manner as if he disapproved of this.